The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, the relatively thick containment casings are relatively heavy, the relatively thin casings enclosed by the fibrous material are lighter but are more expensive to manufacture. The relatively thick casings with fibrous material are both heavier and more expensive to manufacture.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which overcomes the above mentioned problems.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, metal casing, to contain a gas turbine engine rotor blade in a gas turbine engine rotor blade containment region, the metal casing having an inner surface and an outer surface, at least a portion of at least one of the inner surface, or the outer surface, of the metal casing having a plurality of blind apertures extending into the casing from the surface of the casing to reduce the weight of the casing without impairing the stiffness and penetration resistance of the metal casing.
Preferably the at least one portion is at least a part circumferential portion or at least a part axial portion.
Preferably the at least one portion extends completely circumferentially around the metal casing.
Preferably the metal casing has a flange at an upstream end of the metal casing and a flange at the downstream end of the metal casing.
Preferably the at least one portion is a portion of the outer surface of the metal casing between the, flanges at the upstream end and downstream end of the metal casing.
The metal casing may have at least one circumferentially extending rib extending radially outwardly from the metal casing axially between the flanges, the at least one portion of the outer surface of the metal casing is between one of the flanges and the at least one rib or between adjacent ribs. The rib may have a T-shaped cross-section.
Preferably the whole of the outer surface of the metal casing has a plurality of blind apertures.
Alternatively the whole of the inner surface of the metal casing has a plurality of blind apertures.
Preferably at least one portion of the inner surface, or the outer surface, of the metal casing comprises a predetermined pattern of blind apertures.
There may be a first set of blind apertures having a first diameter, a second set of blind apertures having a second diameter and the second diameter is greater than the first diameter. There may be a third set of blind apertures having a third diameter and the third diameter is greater than the second diameter.
Preferably the blind apertures are circular in cross-section.
The blind apertures may be flat bottomed cylindrical blind apertures, part spherical blind apertures or other suitably shaped blind apertures.
Preferably the plurality of blind apertures are arranged in an asymmetrical pattern.
One or more continuous layers of a strong fibrous material are wound around the metal casing.
The metal casing may comprise aluminium, an aluminium alloy, magnesium, a magnesium alloy, titanium, a titanium alloy, nickel, a nickel alloy or preferably from a steel alloy.
An acoustic lining may be provided within the metal casing.
The containment casing may be a fan containment casing, a compressor containment casing or a turbine containment casing.